PHENACODUS and not climbing or grasping organs; the number of toes be- comes reduced, and culminates twice (in the horse and in the Latopterna) in one toe on each foot ; at the same time the ulna be- comes rudimentary and fuses with the radius, and the fibula in the hind-limb undergoes a like reduction. The clavicle is absent even in some of the oldest types ; its presence in Typotherium * is highly remarkable. The tail too, an organ which is long in some of the early forms, gets short in their modern deriva- tives. Coupled with the in- creasing perfection of the Jf foot as an organ used £ merely for the support • of the body, certain in- "j5 teresting changes have o taken place in the "^ arrangement with re- & gard to each other of the several bonelets of the wrist and ankle. It has been held by Cope and others that the truly primitive disposition -of these bones was that pre- sented to us by certain early types, such as MeniscotheTium or the existing elephant or Hyraoo. In these animals there is (see Fig. 112) a serial arrange- 1 This creature is, howerer, sometimes referred to the neighbourhood of the Rodents.